Psoriasis is a common skin disease characterized by marked changes in tissue architecture and by simultaneous activation of a variety of distinct cell types, including epidermal keratinocytes, vascular elements, and leukocytes. The clinical appearance of psoriasis includes red, raised, scaly plaques which are attributed to alterations in the growth and maturation in both the epidermis and dermis of the skin.
A conventional treatment of psoriasis is the oral administration of a psoralen followed by the application of ultraviolet A light (PUVA). A typical treatment using oral PUVA is the administration of eight-methoxypsoralen (8-MOP) followed by exposure to UVA light. Following a treatment, the patient would need to wear protective glasses for twenty-four hours.
A method of treatment preferred by some doctors over oral PUVA is bath PUVA. Bath PUVA involves the delivery of a photosensitizing drug, such as 8-MOP, to the skin followed by the exposure to UVA light. With bath PUVA, the patient soaks in psoralen solution for approximately thirty minutes and then receives an immediate exposure to a therapeutic dosage of UVA light. The patient may soak his or her entire body from the neck below into the psoralen solution, or alternatively, may soak only those portions of the body which are afflicted with psoriasis.
Bath PUVA has proven to be more effective and more pleasurable in treating psoriasis than oral PUVA. In comparison to oral PUVA, bath PUVA has been shown to require approximately one-half as many treatments and at a significantly lower dosage of UVA light. Because there is no systemic absorption of psoralen, bath PUVA does not cause nausea, fatigue, or depression as has been reported with oral PUVA. It reduces the potential for cataract formation, and reduces the possible risk of PUVA-induced cutaneous cancers. Additionally, with bath PUVA, the patient need not wear protective glasses for twenty-four hours after treatment. The effectiveness of oral PUVA is also limited by the body's ability to absorb the medicine from the gastrointestinal tract. In this regard, bath PUVA is preferred since it is not subject to the variances in the absorption of the medicine.
Bath PUVA therapy, however, is also subject to several disadvantages. A single treatment with bath PUVA is approximately three times more expensive than that for oral PUVA. Bath PUVA is also more expensive for the private practitioner since it requires the practitioner to purchase a bathtub and fill and clean the tub for each treatment. The effectiveness of a bath PUVA treatment is also dependent upon the temperature of the water, which is not easily controlled in the bathtub. The effectiveness of bath PUVA also varies due to differences in body size and shape, which prevent uniform coverage with the psoralen solution, and since the coverage of the upper shoulders, torso, and knees is difficult. Furthermore, many patients object to the bath PUVA treatment since it requires them to sit within the confines of a bathtub for thirty minutes with increasingly colder bath water.